Sensors can be used in a variety of industries to monitor equipment. As an example, torque sensors can be used to monitor rotating machine components (e.g., shafts) and output signals representative of torque applied to the monitored components. By comparing measured torques to design specifications, it can be determined whether monitored components are operating within these specifications.
Magnetostrictive torque sensors are a type of sensor that employs magnetic fields for measuring torque. In general, magnetostriction is a property of ferromagnetic materials that characterizes changes in shape (e.g., expansion or contraction) of the material in the presence of a magnetic field. Conversely, magnetic properties of a ferromagnetic material, such as permeability (the capability to support development of a magnetic field within the material) can change in response to torque applied to the material. A magnetostrictive torque sensor can generate magnetic flux that permeates a shaft and it can sense the magnetic flux as it interacts with the shaft. As an amount of torque applied to the shaft changes, a magnetostrictive sensor can output signals representative of torques applied to the shaft based upon the sensed magnetic flux.
However, the distance or gap separating a magnetic torque sensor and a monitored component can change due to vibrations and/or variations in shape of the monitored component during rotation. These changes in distance can cause variations in the magnetic flux sensed by a magnetostrictive torque sensor that are independent of applied torque. Consequently, torque measurements acquired by magnetostrictive torque sensors based upon sensed magnetic flux can deviate from actual torque on a shaft.